This invention relates to a device and a method for marking an arc of a predetermined radius at a square corner. More particularly, this invention relates to a device and a method for marking an arc of a predetermined radius at a square corner of a workpiece so that, by using the arc as a guide for where to make a cut, a rounded corner can be produced.
Carpenters, amateur woodworkers, hobbyists, and others are frequently faced with the task of cutting a workpiece to produce a rounded corner beginning with a workpiece that has a square corner. A person wanting to make a rounded corner usually draws an arc on the workpiece, with the arc serving as a guide for where the cut is to be made. Use of a compass is one of the most precise methods of marking an arc on the workpiece, provided the compass is a good one. Although accurate, it is time-consuming to determine the center of the radius for drawing the arc with a compass. This problem is compounded, of course, when a workpiece has several corners that will be rounded or when several workpieces each have a corner to be rounded. Each corner to be rounded must be individually marked by going through the process of determining the length of the radius, determining the center of the radius, and then drawing the arc. Thus, it is tedious to repeat the same process for each corner to be marked. Compasses are typically able to draw arcs of any size within a certain range. This flexibility can be a disadvantage, however, when arcs of certain standard sizes are used repeatedly. A compass also may leave a hole in the workpiece at the center of the radius. With some types of workpieces this hole can be removed or covered, for example by sanding a piece of wood. However, with some workpieces it would be impossible or impractical to remove or cover the hole. Even if the hole can be removed or covered, it requires time and effort to do so. Further, compasses can be expensive, easily damaged, and easily misplaced.
Another method for marking an arc on a square corner is to place a cylindrical or circular object having the desired radius on the workpiece such that the edges of the workpiece that form the square corner are tangential to the circular edge of the object. With the object thus aligned, an arc is drawn by moving a pencil, pen, nail, or other marking instrument along the edge of the object. Objects such as lids, jars, and cans are often used for such a purpose. However, it is inconvenient to search for an object having the desired radius every time such a mark needs to be drawn. It is also inconvenient to keep a supply of objects on hand for when they might be needed.